1. Field of the Invention
The invention relates to improved techniques for solubilization of coal and, more particularly, to enhancing liquid hydrocarbon yields from solid coal by pretreating the coal to introduce olefinic monomers into the coal structure.
2. Discussion of the Prior Art
In recent years, the production of liquid hydrocarbons from non-petroleum sources has taken on added importance. Thus, with proven world petroleum reserves shrinking, other forms of energy have attracted attention. Much attention has been directed to coal, an abundant fossil fuel in the United States, which can be converted to liquid hydrocarbons at costs approaching current and projected costs for the refining of crude petroleum. Moreover, basic coal conversion technology exists and has been demonstrated on a variety of levels, e.g., pilot plant and full scale commercial plants. However, full development of existing conversion technology is only now underway.
A variety of processes for converting coal to oil or gas have been proposed or used in the past; see, e.g., "Coal Conversion Technology", Chemical Engineering, pp. 88-105 (July 22, 1974), P. A. Lahage et al, "Solubilization of Coal in Organic Media", NASA-TM-75151 (1976) "Coal Conversion--A Review", CHEMSA, 3, pp. 102-104 (1977) and U.S. Pat. No. 4,072,475. A major area of investigation is solvent extraction of coal; see, e.g., U.S. Pat. Nos. 3,018,241, 3,379,638, 3,642,607 and 3,966,582.
One way of increasing solubility of coal has involved graft polymerization of coal; see, e.g., Japanese Kokai 9052-286 and 9025-287, which disclose graft polymerization of coals with water soluble or water insoluble ionically or radically polymerizable monomers. A similar process is disclosed in U.S. Pat. No. 4,033,852, which discloses a process for grafting polymeric side chains onto natural coal employing a free radical catalyst system comprising a source of silver ions and a peroxide polymerization initiator and reacting coal radicals thus produced with an olefinically unsaturated monomer. A charge transfer complex of sodium naphthalide is alternatively employed. Carbonaceous grafts of polymers have also been disclosed in U.S. Pat. No. 3,856,745 and British Specification No. 1,275,619.
A problem with many of the coal stabilization schemes is that high energy input is usually required, as well as utilization of high temperature and high pressure equipment. Alternatively, expensive chemicals and/or solvents are often required, thereby making the widespread use of such techniques economically unfeasible.